High-tensile steel sheet and a method of manufacturing the same excellent bending workability and low-temperature toughness

摘要

PROBLEM TO BE SOLVED: To provide a high-tensile strength steel sheet which is obtained by imparting superior bending property and low temperature toughness to a steel sheet having a tensile strength of ≥1,150 MPa and a sheet thickness of about 7-50 mm.;SOLUTION: The high-tensile strength steel sheet has a steel composition comprising, by mass%, 0.10-0.25% C, 0.05-1.5% Si, 0.5-2.0% Mn, 0.3-2.2% Cr, 0.2-1.4% Mo, 0.001-0.024% V, 0.005-0.1% Al, 0.0005-0.006% N, ≤0.02% P, ≤0.005% S, and 0.0003-0.003% B, wherein formula (1) is satisfied, and the balance Fe with inevitable impurities. The high-tensile strength steel sheet has a steel structure, wherein martensite structure has a volume fraction of ≥95%, and the average grain diameter of old austenite grains is ≤20 μm, in the martensite structure, and has a tensile strength of ≥1,150 MPa. 0.60≤[% Cr]+0.6[% Mo]-9.5[% V]≤1.30...(1).;COPYRIGHT: (C)2012,JPO&INPIT